The invention concerns a method for the control of an automatic transmission of a motor vehicle driven by an internal combustion engine with an exhaust gas catalyst, wherein, for a more rapid warm-up of the catalyst, a warm-up gear shift program is provided, in accord with the generic concept more closely defined in claim 1.
For the minimizing of environmentally damaging emissions, modern motor vehicles possess an exhaust gas catalyst located following the internal combustion engine. Catalysts, installed in such a manner, only become fully active when heated to their operating temperature. In order to assure an optimal cleaning of the exhaust gases, the catalyst must he heated up as rapidly as possible after a cold start. The rapid start, where automatic transmissions are concerned, is supported by specified shift positions, which are related to progressively higher rotational speeds of the motor.
In this matter, warm-up programs have been made known within the practice, which are activated at higher RPM""s, but wherein the duration of such programs has always presented problems. In case, for instance, a warm-up program is too short, then the exhaust gas catalyst does not attain its necessary operating temperature and the level of the contaminating materials emitted from the vehicle are higher than desired. If the warm-up program lasts too long, then the driving mode is unnecessarily carried out too long at a high fuel consumption and with limited driving comfort.
DE 39 28 814 C2 discloses a control apparatus for a self shifting transmission for a motor vehicle with an exhaust gas catalyst, wherein the shifting stages can be chosen by the driver for either manual operation or automatic, on at least an optimized driving-requirement and/or an optimized loading basis. If, by means of a temperature sensor, the conditions of a cold start of the motor vehicle are signaled, then, a warm-up program is activated for a specified time period, or as long as the cold start conditions remain in force. This so activated warm-up program permits only such driving conditions as are in accord with the higher preset exhaust gas quantities and energy flow as are specified in the optimized shift program.
This procedure leads to a quick attainment of the temperature required for a sufficient for satisfactory conversion rate of exhaust gas contaminating materials. However, the specification for a definite running time for the warm-up program neglects to take into consideration, that the catalyst warms more quickly or slower in proportion to the manner of driving.
In order to align the warm-up program more nearly in accord with the factual conditions, there is provided, besides the expiration of a predetermined time as a termination criterium for the warm up program, also the attainment of a specified temperature of the motor, of the transmission, or of the catalyst. Since, in practice, the warm-up periods of the motor, the transmission and the catalyst generally can be widely differing, this procedure as compared to the actual motor and/or transmission temperatures is subject to substantial errors.
Values most nearly approaching reality, can only be achieved by means of a proposed determination of the actual temperature of the catalyst. This requires, however, extensive, costly and sensitive instrumentation.
DE 41 14 033 C2 makes known another procedure for the control of the change of gear shift positions in a motor vehicle, wherein, during the warm-up phase of the motor, stored shift curves are modified in such a way, that the interchange of gears at higher speeds, that is, at higher RPM of the internal combustion engine, is carried out in accord with the warm-up phase.
The duration of the warm-up program depends, in this procedure, on a ratio between motor cooling water temperature, as determined by a temperature sensor, and a preset operational temperature, wherein the warm-up phase is assumed to be terminated, when the actual motor cooling water temperature has reached the temperature of its said preset operational temperature.
Since, also in this case, the unreliable temperature values of the motor cooling water can be brought forward as a criterium for terminating the warm-up program, once again, the real conditions are not sufficiently approximated.
The purpose of the present invention is to make available a method for the control of an automatic transmission of a motor vehicle which is driven by an internal combustion engine having an exhaust gas catalyst, with which a warm-up gear shift program to bring about a more rapid warm-up of the exhaust gas catalyst, wherein higher gear shifting points for gear changes remain activated, only for such a time, until the exhaust gas catalyst achieves it optimal operational temperature. In this way, at the earliest possible moment, a return to more quiet and fuel saving gear ratio can be made.
In accord with the invention, this purpose is achieved with a method in accord with the characterizing features of claim 1.
The logic of the method in accord with the invention, has a starting point, wherein it is signaled, that the exhaust gas catalyst is warmed, depending on the exhaust gas quantity which flows through it, wherein said exhaust gas quantity is a function of the speed of rotation of the motor and the motor torque.
The exhaust gas quantities can be very simply determined empirically and reliably for all possible conditions of operation, and stored in a computer of the electronic transmission control apparatus. Since the measured value of the temperature of the motor, upon the start of the internal combustion engine, under the best conditions, agrees with the temperature of the exhaust gas catalyst, the invented method is provided in an advantageous way with reliable data, which data, in a predominate manner, reflect the actual conditions. Thereby the invented method makes possible, that the exhaust gas catalyst is more quickly warmed up to its normal operating temperature, whereby a desirable lessening of the contaminant emission is achieved.
Additionally, however, the duration of the warm-up shift program is so determined, that the RPM increasing action of the warm-up program is held to the least possible time. By this means, early in a shift program, the shift can be carried out at lower gear ratios, which action makes possible a desirable driving mode with low fuel consumption.